Continuously adjustable resistor



Mirch 1955 J. GRAYBEAL ET AL 2,704,800

CONTINUOUSLY ADJUSTABLE RESISTOR Filed Dec. 28, 1955 2 Sheets- Sheet 1 JAKE GRAYBEAL MARTIN K. LILLEBERG INVENTORS March 22, 1955 J. GRAYBEAL ET AL 2,704,

CONTINUOUSLY ADJUSTABLE RESISTOR Filed Dec. 28, 1955 2 Sheets-Sheet 2 v JAKE GRAYBEAL MARTIN K. LILLEBERG 48 INVENTOR.

' FIG-8 United States Patent CONTINUOUSLY ADJUSTABLE RESISTOR Jake Graybeal, Seattle, and Martin K. Lilleberg, Mercer Island, Wash., assignors to United Control Corporation, Seattle, Wash., a corporation of Washington Application December 28, 1953, Serial No. 400,723

8 Claims. (Cl. 201-62) This present invention relates to the general art of variable resistances and more particularly to potentiometers and the like which are made to serve the need of potentiometers where it is necessary to have a very compact unit and one which gives precise settings throughout the entire length of the resistance wire.

There are many fields, particularly in the construction of electronic equipment, where it is very desirable to provide the current portioning or controlhng means in a very small unit. Typical of such fields is the manufacture of aircraft, guided missiles, proximity fuses and the like, where space is at a great premium. Variable resistances made after the teachings of this present invention can be made very small in diameter and relatively short and yet have the desirable high electrical characteristics. The same principles may be employed in a potentiometer or the like in which the coil has a relatively large diameter and short length so that agam it may be employed in a minimum space for the electrical capacity of the equipment. It has been found that in highly developed electrical and particularly electronic equipment that the ordinary coil by coil steps of varying resistance does not give the accuracy of controls that are so often necessary. This present invention is pro-- vided with means so that the slidable contactor member engages the resistance coil throughout its entire length as distinguished from a step from one coil to the next coil arrangement. This characteristic makes it possible to give a high degree of adjustment to critical electrical circuits. It is therefore believed that the property of high electrical values in a small unit having an actual continuously variable electrical resistance offers a very effective solution to many of the heretofore perplexing problems with which designers were confronted. It is submitted therefore that this present invention provides a truly worth while advantage in this specialized field.

The principal object of this invention is to provide a continuously adjustable variable resistance, of the wire coil type, which admits of producing the same in truly miniature proportions.

A further object of this invention is to provide a coil type variable resistance in which the contactor brush travels around the coil so that it may contact the resistance wire throughout its entire length.

A further object of this invention is to provide a very compact type of potentiometer resistance in which very small changes can be accurately made.

A further object of this invention is to provide a round coil type of potentiometer in which a setting can be made verly readily to any portion of single turn of the resistance cor Further objects, advantages and capabilities will be apparent from the description and disclosure in the drawings, or may be comprehended or are inherent inthe device.

In the drawings:

Figure l is a perspective view illustrating a fully assembled potentiometer made after the teachings of this invention, and showing the employment of a small diameter coil;

Figure 2 is an exploded bracketed view showing the various parts of this potentiometer;

Figure 3 is a bracketed perspective view showing the mounted bushing and the mounted collar employed with. the same to facilitate the mounting of the unit;

Figure 4 is a perspective view showing a portion of a potentiometer made after the teachings of this invention with the same cut away in part and sectioned in part to better illustrate the construction of the same;

Figure 5 is a typical sectional view showing this unit, the illustration thereof being somewhat exaggerated for clarity of illustration;

Figure 6 is a fragmentary longitudinal sectional view illustrating the manner in which the contactor brush engages the adjacent turn of the coil and the manner of insulating the coil from the conductive core;

Figure 7 is a perspective view, partly in section, illustrating the manner in which the contactor brush is secured into its supporting nut; and

Figure 8 is a diagrammatic viewing illustrating one form of circuit to which this equipment is particularly adapted.

Referring more particularly to the disclosure in the drawings, the numeral 10 designates the core upon which the resistance wire coil 12 is wound. The core is formed of some suitable material as copper or copper bearing alloy having electrical conductivity of a high order. The core, which is of uniform diameter throughout the portion covered by coil 12, is reduced at one end to provide the terminal portion 14, a portion of which extends outwardly so it can clear the other part of the unit and make it available for the attachment of one of the connecting electrical leads. In this present showing core 10 is illustrated as of minimum diameter and having considerabile length. The resistance wire from which coil 12 is wound will vary in diameter, total length and material so as to suit it to the circuit with which it is to be used.

If, however, the mounting requirements indicate the desirability of a flat short coil then the diameter may be very appreciably increased and the length shortened so as to provide the same length of resistance wire 12.

In this modified form the various parts would function similarly but would of necessity be changed in their general proportions.

In the very compact unit to which this type of equipment is best adapted, the material used in the resistance wire should be one that is relatively close in the electromotive series to the contactor brush 16 which is adapted to engage the coil substantially throughout its entire length as it has been found that the minimum deterioration of the units occur when these two members cause the minimum reaction between themselves. Experience has proven that some of the gold bearing alloys are best for brush 16 and this, of course, will to a degree indicate the form of resistance wire 12 that is best employed in the unit.

The manner in which coil 12 is wound on the core is probably best illustrated in Figures 5 and 6. When uncovered or bare resistance wire is employed it is desirable that core 10 be initially coated with a layer of insulating enamel as 18, and that this layer be cured. When this layer of enamel is fully set a second layer of enamed 20 is applied and when it has dried to the point where it is just tacky but will not flow readily, coil 12 is machine wound on the core in a spaced-apart turn arrangement. As the coil is wound the necessarily applied tension on the wire will cause the same to imbed itself in the softish layer of insulating enamel 20 until it substantially comes to rest upon the cured enamel layer 18. This will cause the yieldable enamel 20 to swell up around the wire as is indicated at 22. When the winding has been completed the coil is then baked to set the second layer of enamel and then the coil is buffed so as to bare the wire and remove any irregularities in the second coat of enamel in order that brush 16 will at all times be able to bear directly on the Wire. One end of coil 12 is secured as by spot welding at 24 to the metal of the core 10.

The other end of coil 12, of necessity, must be insulated from core 10 and this is assured by the insulating bushing 25, the construction of which is best illustrated in Figure 5. Disposed concentrically around the reduced diameter portion of the insulating bushing 25 is the conductor bushing or sleeve 26 and it is to this bushing that the opposite end of coil 12 is secured as by spot welding thereto at 28.

Resistance coil 12 and its associated parts must be spaced away from and in coaxial arrangement with the covering sleeve 30 which must be made of conductive material as it is used as a conductor for the current contacted by brush 16. A preferred positioning for coil 12 is provided by means of an insulating member 32 which is threaded at 33 to engage the threaded interior of sleeve 30. A bore portion 34 of nut 32 establishes additional coaxial support for core 10.

Adapted to operatively engage the interior threads 36 of sleeve 30 is a contactor nut 38 which is provided with co-acting exterior threads 40. Nut 38 is preferably cut away at 42 so as to provide the abutting surfaces 43 and 44 which are disposed for operable engagement with wrench 46. The contactor nut 38 provides the mounting for the contacting brush 16. This brush, which is preferably made from a material having high resistance to corrosion, is provided with a central contact portion 48, which portion is relatively thin and curved after the showing of Figure 6. The two ends of the brush member however are cylindrical and one of these ends is fitted in a drilled hole 50, which hole is substantially wire size and after the brush is put in place the metal adjacent this hole is preferably pruned to provide a secure anchroage for the brush. The opposite end of the brush is also cylindrical and is substantially centered within the round opening 52. This opening is considerably larger than the floating end 53 and serves to limit the movement of brush 16 and to generally hold it in its operating position at all times.

Disposed concentrically with the axis of core is the wrench member 46. The form of this member is probably best shown in Figures 2 and 4. It consists essentially of two ring portions 60 and 61 which are of a diameter so that they will freely glide upon the interior threads 36 of sleeve 30. This provides the centering and positioning means for wrench 46 in part. Rings 60 and 61 are joined by a curved bar portion 64 which, in effect, is a segment of a tube which normally rides freely on threads 36. Additional axial positioning of wrench 46 is provided by shaft portion 66, formed as part of the wrench and which is supported by the mounting bore 71 of bushing 70. This bushing is externally threaded at 73 to engage threads 36 of sleeve 30 and seat flange 74 tightly against the end of the sleeve. The opposite end of the mounting bushing is threaded at 76 to receive the mounting nut 78. The bushing is held in position on shaft 66 by a snap ring 75 adapted to seat in the annular groove 77. Shaft 66 extends sufiiciently above the panel or mounting surface so that a screw driver can engage kerf 68 and thus turn wrench 46 and adjust the device.

Referring to Figure 8, the conventional diagram symbol of potentiometer is indicated. The negative lead 90 is taken from the reduced portion 14 of core 10. The end of coil 12 is bonded to core 10 at 24 and core 10 and its extension 14 form the conductor. The opposite end of coil 12 is bonded at 28 to sleeve 26 which serves as a convenient attachment for the positive lead 91. The variable lead 92 is secured in some convenient manner to sleeve 30. The flow of current is through sleeve 30 to the contactor nut 38 then through brush 16 to contact portion 48 which rides on adjacent turns of coil 12. Contact portion 48 acts, to a degree, as does the arm of a potentiometer in that it varies the point of contact as it is moved along the coil. In this instance, however, there is a distinct advantage over the conventional rider or contact arm which actually engages the resistance coil in a line of contact and thus it varies the proportioning of the current in one turn steps. With this present arrangement, however, nut 38 is disposed for revolution about the coil and is moved into successively angular positions by wrench member 46. Thus, in effect, the point of contact is continuously variable just as though the wire were straight and a sliding contact were moved along it. This arrangement makes it possible to have an infinite number of settings and due to the fact that the contact is moved around the coil by a fine thread 36 a very fine vernier type setting is achieved. Such niceties of adjustment are greatly sought after in many fields of electronics.

Attention is drawn to the fact that throughout the drawings the separate turns of the wire forming coil 12 are shown as spaced. This is a desirable arrangement if bare wire is used. If, however, it should be desirable to have the coils quite close together then the coil might be formed of enameled insulated wire and this construction has been indicated in Figure 6 wherein a semi-circular portion of the insulation as 94 is shown. It naturally follows that if insulated wire is used in order to gain the tight spacing of the coils the upper surface of the insulation must be buffed off so that contact member 48 will be able to engage bare wire. This general construction is indicated in Figure 6. If requirements indicate the need, however, the insulation carried by the wire at 94, of each of the adjacent turns, could be in an abutting relationship.

It is believed that it will be clearly apparent from the above description and the disclosure in the drawings that the invention comprehends a novel construction of a continuously adjustable resistor.

Having thus disclosed the invention, we claim:

1. A coil type variable resistance for a potentiometer or the like, comprising: an elongated, generally cylindrical core of high electrical conductivity having a terminal portion at one end, a resistance wire wound on said core in a helical path, means insulating said resistance wire from said core, leaving the outer surface of the resistance wire bare, except at the end of said wire opposite the terminal portion of said core where the wire and core are in electrical contact, means forming a terminal for the other end of said resistance wire insulated from said core, a tube-like sleeve forming a third terminal positioned encircling said core in spaced, coaxial relation thereto and insulated supporting means between the sleeve and the core, the interior of said sleeve having threads matching the turns of said resistance wire, a rotatable connector nut positioned encircling said core, said connector nut having threads on its outer surface matching and engaged with the threads on the inside of said sleeve so as to follow a helical path along said resistance wire when rotated, a wrench having a ring at each end rotatably mounted on said core by means insulating the wrench and core, said nut having a slot therethrough splitting the nut and the portion of said wrench intermediate said rings being slidably positioned in said slot, means for rotating said wrench about the axis of said core whereby said nut is rotated therewith, and brush means between said coil and said resistance wire forming a continuous contact therebetween.

2. A continuously adjustable coil type variable resistance, comprising: an elongated, generally cylindrical core, a resistance wire wound on said core in a helical path, means forming a terminal at least at one end of said resistance wire, a conductor member having a brush in contact with said resistance wire, and mechanical means operable to obtain relative movement between said conductor member and said core so that relative rotary movement is obtained between said brush and said resistance wire in which the brush moves from end to end of said resistance wire contacting in turn continuously every portion thereof, means forming a terminal for said conductor member, said core having high electrical conductivity and said means forming a terminal at least at one end of said resistance wire including an electrical contact between one end of said core and one end of said resistance wire and the other end of said core having a portion of reduced diameter making a formed terminal, and there being insulating means between all adjacent surfaces of said core and said resistance wire except at said electrical contact.

3. A continuously adjustable coil type variable resistance, comprising: an elongated, generally cylindrical core, a resistance wire wound on said core in a helical path, means forming a terminal at least at one end of said resistance wire, a conductor member having a brush in contact with said resistance wire, and mechanical means operable to obtain relative movement between said conductor member and said core so that relative rotary movement is obtained between said brush and said resistance wire in which the brush moves from end to end of said resistance wire contacting in turn continuously every portion thereof, means forming a terminal for said conductor member, said conductor member having a rotatable connector nut positioned encircling said core, said mechanical means including a tube-like sleeve forming said last-mentioned terminal positioned encircling said core in spaced, coaxial relation thereto and supporting means between said sleeve and said core, the interior of said sleeve having threads matching the turns of said resistance wire, said connector nut having threads on its outer surface matching and engaged with the threads on the inside of said sleeve.

4. A continuously adjustable coil type variable resistance, comprising: an elongated, generally cylindrical core, a resistance wire wound on said core in a helical path, means forming a terminal at least at one end of said resistance wire, a conductor member having a brush in contact with said resistance wire, and mechanical means operable to obtain relative movement between said conductor member and said core so that relative rotary movement is obtained between said brush and said resistance wire in which the brush moves from end to end of said resistance wire contacting in turn continuously every portion thereof, means forming a terminal for said conductor member, said conductor member having a rotatable connector nut positioned encircling said core and resting on said resistance wire.

5. The subject matter of claim 2 in which said insulatmg means is a first lower coat of insulating material on said core on which said resistance wire rests and a second upper coat of insulating material in which said resistance wire is embedded, the outermost surface of said resistance wire being bare.

6. The subject matter of claim 2 in which a second terminal is formed for said resistance wire by a conductor bushing positioned on said core adjacent said formed terminal and insulated from said core, said conductor bushing having electrical contact with the other end of said resistance wire.

7. The subject matter of claim 3 in which said nut has a slot therethrough splitting the nut and said mechanical means includes a wrench having a ring at each end rotatably mounted on said core by means insulating the wrench and the core, the portion of said wrench intermediate said rings being slidably positioned in said slot.

8. The subject matter of claim 7 in which said intermediate portion of said wrench has the shape of a segment of a cylinder with a smooth exterior surface riding on the threads on the interior surface of said sleeve, said wrench having an end portion positioned at one end of said core adapted to be engaged to rotate said wrench, there being a bushing on said end portion of said wrench permitting rotation of the wrench therein, said bushing having an annular shoulder and having a threaded end outside of said shoulder and a securing nut positioned on the threaded end for securing a supporting member between the securing nut and shoulder, and said bushing having a second threaded end inside of said shoulder forming the supporting means for the adjacent end of said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 1,491,345 Gargan Apr. 22, 1924 

